1. Field of the Invention
The present invention relates generally to medical devices and treatment methods. More particularly, the present invention relates to methods and apparatus for treating cardiac arrhythmias with vibrational energy.
Cardiac arrhythmias, including ventricular tachycardias and ventricular fibrillation, are a leading cause of morbidity and death in Western societies. A very successful technique for treating such ventricular arrhythmias is generally referred to as “ventricular cardioversion and defibrillation,” where an electrical current is applied across the chest to synchronize cardiac rhythm. The use of external cardioversion and defibrillation equipment, i.e. where electrode paddles are placed externally on the chest and where relatively high currents are applied, has been very effective, but of course requires the availability of both the equipment and an operator capable of using the equipment. More recently, implantable cardioverter defibrillator (ICD) devices have come into use, which are programmed to automatically intervene after the onset of an arrhythmia. ICD's stabilize the cardiac rhythm by delivering cardioversion, defibrillation, and pacing therapies as needed. Such ICD's have been shown to improve survival and have become the standard of therapy in patients at risk. While above references have been made to ventricular arrhythmias, atrial arrhythmias are also stabilized with ICD devices.
ICD's, however, do suffer from certain disadvantages. At present, ICD designs require one or more electrical leads to be implanted on or within the heart in order to provide pacing, cardioversion and defibrillation currents. Such lead placement requires skilled personnel and subjects the patient to radiation during the implantation procedure. The implanted leads are subject to failure and may cause cardiac perforation, thrombo-occlusion, and infection. Lead failure due to fracture or insulation break has been reported to occur in a significant fraction of the patient population after several years. Present ICD's also require a relatively long time to charge capacitors, typically from 10–15 seconds, potentially delaying treatment after a potentially lethal arrhythmia is detected. Delay in treatment also requires higher energy delivery to be successful. Moreover, many patients who have received ICD's find that the electric shocks are painful, and the unpredictable nature of the ICD firing can cause anxiety and fear.
Atrial fibrillation is more common than ventricular fibrillation and tachycardia, but is not directly lethal, although it is associated with thrombus formation in the atrial appendage and has the potential for causing embolic stroke. Atrial fibrillation is characterized by rapid and disorganized activity in both the left and right atria. There is absence of atrial contraction and often atrial enlargement. The lack of coordinated atrial contraction can reduce cardiac output which can exacerbate other heart conditions. While not usually fatal, patients in atrial fibrillation may experience chest pain, fatigue, lightheadedness, and shortness of breath. The rapid and irregular heart rate and palpitations associated with atrial fibrillation can be very distressing to patients.
The treatment of atrial fibrillation is generally similar to that for ventricular fibrillation and tachycardia, i.e. electrical defibrillation. In other cases, drugs may be sufficient to convert atrial fibrillation to normal sinus rhythm.
Since atrial fibrillation is not directly lethal, episodes occur frequently, and the patients are conscious and alert, there is a significant reluctance for patients to undergo electrical defibrillation, either externally or using implantable devices. For external defibrillation, patients generally require deep sedation or general anesthesia. Although implantable atrial defibrillators have been developed, patients have found such treatment unacceptable and the device is not currently marketed.
Patients suffering from atrial fibrillation, ventricular tachycardia, and ventricular fibrillation (abnormally fast heart rhythms), typically have structural heart disease which also makes them prone to have abnormally slow or absent heart rhythms such as sinus arrest, sinus bradycardia, heart block, asystole, and the like. Moreover, the abrupt termination of abnormally fast heart rhythm is often followed by a transient period of abnormally slow or absent heart rhythm. For these reasons, both external and implanted defibrillator devices for the termination of abnormal fast heart rhythms incorporate the capability to terminate slow or absent heart rhythms, referred to as pacing. For ICD devices, such pacing capability ordinarily requires electrical leads implanted within the heart. For external devices, such pacing capability employs the delivery of transcutaneous electrical energy through chest electrodes, which is very painful, similar to the pain associated with the delivery of electrical energy for defibrillation.
For these reasons, it would be desirable to provide improved ICD's and external defibrillators which are free from some or all of the deficiencies noted above. In particular, it would be desirable to provide such ICD's and external defibrillators which do not rely on the application of electrical current in order to achieve defibrillation. It would be further desirable to provide ICD's and external defibrillators which do not require implantation of components into the heart. In particular, it would be desirable if ICD's could be implanted remote from the heart and project energy or otherwise interact with the heart without actual contact. Such ICD's should be easy to implant, have few associated complications, be able to treat with little time delay, and provide cardioversion and defibrillation without significant pain or other undesirable side effects. Additionally, it would be desirable to provide ICD's and external defibrillators for the treatment of both ventricular and atrial rhythms that are abnormally fast, slow, or absent in a manner which is more acceptable to patients than present systems. At least some of these objectives will be met by the invention as described herein below.
2. Description of the Background Art
Patents describing the treatment of arrhythmias using mechanical shock therapy include U.S. Pat. Nos. 6,439,236; 6,408,205; 6,330,475; 6,110,098; 5,433,731; and 4,651,716; as well as PCT Applications WO 03/070323 and WO 99/061058. Other patents of interest include U.S. Pat. Nos. 6,233,484; 5,800,464; 5,871,506; 5,292,338 and 5,165,403. Medical publications discussing the effects of ultrasound energy and/or mechanical action on the heart include:    The Antiarrhythmics Versus Implantable Defibrillators (AVID) Investigators: A comparison of antiarrhythmic drug therapy with implantable defibrillators in patients resuscitated from near fatal ventricular arrhythmias. N Engl J Med 1997; 337: 1576–1583.    Bardy G H, Cappato R., Smith W M, Hood M, Rissmann W J, Gropper C M, Ostroff H. The totally subcutaneous ICD system (The S-ICD). PACE. 2002; 24,578.    Camm A J, Murgatroyd F D, Nonpharmaceutical treatment of atrial fibrillation. In Atrial Fibrillation. Facts from Yesterday—Ideas for tomorrow. Futura Publishing Company, Inc., Armonk, N.Y., 1994.    Dalecki D, Keller B B, Raeman C H, Carstensen E L. Effects of pulsed ultrasound on the frog heart: I. Thresholds for changes in cardiac rhythm and aortic pressure. Ultrasound in Med. & Biol. 1993; 19:385–390.    Dalecki D, Keller B B, Carstensen E L, Neel D S, Palladino J L, Noordergraaf A. Thresholds for premature ventricular contractions in frog hearts exposed to lithotripter fields. Ultrasound in Med. & Biol. 1991; 17:341–346.    Dalecki D, Raeman C H, Carstensen E L. Effects of pulsed ultrasound on the frog heart: II. An investigation of heating as a potential mechanism. Ultrasound in Med. & Biol. 1993; 19:391–398.    Ellenbogen K A, Wood M A, Shepard R K, Clemo H F, Vaughn T, Holloman K, Dow M, Leffler J, Abeyratne A, Verness D. Detection and management of an implantable cardioverter defibrillator lead failure. JACC. 2003; 41:73–80.    Feldman A and Bristow M. Comparison of medical therapy, resynchronization and defibrillation therapies in heart failure trial (COMPANION). Presented at ACC 2003 Late Breaking Clinical Trials.    Franz M R. Mechano-electrical feedback in ventricular myocardium. Cardiovascular Research. 1996; 32:15–24.    Gibbons R J, Antman E M, Alpert J S, Gregoratos G, Hiratzka L F, Faxon D P, Jacobs A K, Fuster V, Smith SC Jr. ACC/AHA/NASPE 2002 guideline update for implantation of cardiac pacemakers and antiarrhythmia devices: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/NASPE Committee to Update the 1998 Pacemaker Guidelines). Circulation. 2002; 106:2145–2161.    Hu H, Sachs F. Stretch-activated ion channels in the heart. J. Mol. Cell Cardiol. 1997; 29:1511–1523.    Kohl P, Hunter P, Noble D. Stretch-induced changes in heart rate and rhythm: clinical observations, experiments and mathematical models. Progress in Biophysics & Molecular Biology. 1999; 71:91–138.    Kohl P, Nesbitt A D, Cooper P J, Lei M. Sudden cardiac death by Commotio cordis: role of mechano-electrical feedback. Cardiovascular Research. 2001; 50:280–289.    Lee K L, Hafley G, Fisher J D, Gold M R, Prystowsky E N, Talajic M, Josephson M E, Packer D L, Buxton A E. Effect of implantable defibrillators of arrhythmic events and mortality in the multicenter unsustained tachycardia trial. Circulation. 2002; 106:233–238.    Moss A J, Zareba W, Hall W J, Klein H, Wilber D J, Cannom D S, Daubert J P, Higgins S L, Brown M W, Andrews M L. Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med. 2002; 346:877–933.    Niehaus M, Pirr J, De Sousa M, Houben R, Korte T, Eick O J. Non-contact cardiac stimulation with focused ultrasound pulses. PACE 2003: 26:1023.    Nolte S, Doring J H, Frey A. Mechanically induced ventricular extrasystoles in the isolated perfused guinea-pig heart. Arzneim.-Forsch/Drug Research. 1987; 37(11): 1025–1029.    Reiter M J. Effects of mechano-electrical feedback: potential arrhythmogenic influence in patients with congestive heart failure. Cardiovascular Research. 1996; 32:44–51.    Smailys A, Dulevicius Z, Muckus K, Dauksa K. Investigation of the possibilities of cardiac defibrillation by ultrasound. Resuscitation. 1981; 9:233–242.    Tacker, W A. Fibrillation causes and criteria for defibrillation. In Defibrillation of the heart. Tacker, W A, ed. Mosby-Year Book, Inc., St. Louis, Mo. 1994.